* {
    padding: 0;
    margin: 0;
}

body {
    background: #151515;
}

.box {
    background: #1b1b1b;
    width: 390px;
    height: 450px;
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}

.title {
    color: white;
    height: 40px;
    margin: 20px 40px;
    line-height: 40px;
    /* 用text-align可以直接让文字居中 */
    text-align: center;
    margin-top: 40px;
}

.change-bg {
    background: linear-gradient(to bottom, #2f2f2f, #242424);
}

.username {
    overflow: hidden;
    width: 320px;
    margin: 20px auto;
}

.login-icon {
    float: left;
    height: 40px;
    width: 40px;
    border: 2px solid #2f2f2f;
    display: flex;
    justify-content: center;
    align-items: center;
    color: #848384;
    border-right: none;
    /* background: #282828; */
    border-radius: 5px 0 0 5px;
}

.login-txt {
    float: left;
    height: 40px;
    width: 270px;
    /* background: #282828; */
    outline: none;
    border: 2px solid #2f2f2f;
    font-size: 16px;
    color: #848384;
    border-radius: 0 5px 5px 0;
    text-align: center;
}

.login-txt:hover {
    border-color: #2d8f3d;
    color: #26b33d;
}

.login-txt:focus {
    border-color: #2d8f3d;
    color: #26b33d;
}

.login-btn {
    height: 40px;
    width: 310px;
    margin: 20px 40px;
    background: linear-gradient(to bottom, #2f2f2f, #242424);
    border: 2px solid #2f2f2f;
    color: #848384;
    border-radius: 5px;
}

.login-btn:hover {
    border-color: #2d8f3d;
    color: #26b33d;
}